4 reasons why the shortest stroke length is best

The influence of the stroke length is not well understood. Press operators, however, have an inclination because, most often, they will comment: “This job can only run in this press” or, “We can’t run this job as fast as it should,” without being able to articulate why.

There may be a variety of reasons, but most often, it is related to the integrity of the press and the stroke length. Many stamping operations happen under less than ideal conditions. One detail often overlooked or misunderstood is the impact of the stroke length.

So why use the shortest possible stroke in metal stamping? Well, because it could save your stamping operations time, money, resources, and effort. This includes reduction of wasted time, smaller dynamic forces in press structure, better forming, and longer tool life.

In this article, we'll break down these four main reasons why using the shortest stroke for stamping processes is the best:

1) Reduce Wasted Time

Unnecessary ram movement is wasting time and energy. A shorter stroke reduces thermal losses and guides wear. 

2) Smaller Dynamic Forces in Press Structure 

Moving the ram and the upper tool section up and down a shorter distance in a given amount of time reduces the harmful forces within the press frame and drive system.

3) Better Forming

Time allocated to shaping metal is most critical. More time for forming yields better results and a more stable process. The forming time is inversely related to the stroke length. This is illustrated in the following example:

 

ram position graph-1

As can be seen in Figure 1, the ram position curve for the 12 inch stroke (Orange) intersects the material thickness line (0.25 inch) at 163 degrees, while the 6 inch stroke (Yellow) intersects this line at 156 degrees.

Results of longer forming time (6 inch):

  • 7 additional degrees of crank rotation to the forming or cutting process
  • 23 milliseconds extra forming time at 50 Strokes per Minute (SPM)
  • 42% increase in overall forming time

Advantages of longer forming time (6 inch):

Longer forming times, meaning you press has more time to focus on the actual forming and less time wasted on the ram movements between crank rotations. 

4) Longer Tool life

Shorter strokes reduce the velocity at the point where the die punches make contact with the material. As a result, cutting punches are less likely to chip or get dull. This is illustrated in Figure 2:

 

ram velocity graph-1

* The 40mm link motion was included to illustrate that its forming time is shorter and the impact is higher. However, this comes at the cost of significantly higher forces within the press structure.

If a mechanical feed is coupled to a link motion press, the working portion of the stroke is half of the stroke of an eccentric press.

In the example above, the working portion between 90 and 180 degrees is only 10 inches. Hence the comparison should be made with a 20mm stroke of an eccentric press. 

The optimal stroke is always the shortest stroke possible

A careful analysis of the part to be shaped and the feed system will provide insight into what the shortest stroke length possible for a given process can be. At any point during the crank rotation, one of the following occurs:

  • Cutting, forming, etc.
  • Feeding
  • Piloting
  • Gap opening/closing to provide clearance for feeding

Other operations, such as inspection or welding, can be incorporated in the cycle. This should only be considered when the value-add is greater than the reduction of efficiency at the press. In the trade-off consideration, all factors discussed above need to be considered.

A shorter stroke yields:

  • Fewer punch breakages in tool
  • Longer interval between tool sharpening 
  • Better forming results
  • Longer press life
  • Less vibration
  • Less noise
  • Fewer nuisance faults

Sangiacomo Presses Americas is ready to help you optimize your stamping operations with our adjustable stroke press.

Still considering your options? Our helpful sales reps will gladly answer any questions or concerns you have about our presses.

Contact us today at 256-275-4701 or email us at info@sangiacomo-presses.com.

 

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